Amit:

Well I have been conducting some research work on Ga implanted Silicon
system and I know why you are seeing this problem. This may be caused due
to two factors:

* If you are using HF-HNO3-DI that you had mixed more than 40 min (this
time is dependant on the concentration/ratio of etchants) prior to etching
you tend to see these brownish stain. Try to mix your etchant just before
you are going to etch.

* Check the ratio of HF-HNO3-DI of your etchant, you may be in the staining
regions (refer tot he ternary diagram).

Also if you can email me a brief write-up as to what you are doing and what
you are trying to achieve may be I can suggest some receipes. Are you using
either DC bias or UV activation while etching.

Regards
Jayant
 **********************************************************
Jayant Neogi
Director: Research and Development
NORSAM Technologies (http://www.norsam.com)
Portland, Oregon
Ph# (503) 807-3367 (work)
************************************************************

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> From: Amit Shiwalkar   
> To: [email protected]
> Subject: Help on Si-Etch Phenomenon.
> Date: Friday, August 21, 1998 6:56 AM
>
> Hello,
>       I have done some etching ( isotropic ) on Si with HNO3 (63%)&
> HF(49.3%) mixture and using DI H20 as diluent. On certain occasions it
was
> observed that there were blackish-brown marks ( like charring ) on the
> wafer. This wafer was P-type. Also if the etching was done using glacial
> ascetic acid as diluent then on no ocassion were these brown marks
> observed. Also these marks were not consistently observed even in the H2O
> diluent recipe.
>       I would appreciate if anybody could give me any references or
> suggestions about the cause of this phenomenon. Classic recipe handbooks
> like Ghandhi, Donovan & Burger etc. do not mention any such phenomenon.
>       Note that even in the case of glacial ascetic acid as the diluent,
> some places(where water droplets were retained)  were charred in the step
> where etching was stopped by a dip in DI water.
>
> Thanking you all in advance
>
> Regards
> Amit Shiwalkar
>
>
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> Amit Shiwalkar                         Dept. Of Bio-Medical Engineering.
> 3,Vasant,                              IIT Bombay.
> Carter Road,                           Powai, Bombay-400076
> Khar,
> Bombay(Mumbai)-400052
> INDIA.
>
>
>                    Email: [email protected]
>
> " Reality Is a Figment of IMAGINATION "
>                               ----------- Amit Shiwalkar
>
>
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